Pros:

-Makes everything darker

-You have to rely on your team mates more

-If you want to see better in the dark you have to have your first aid in your hands ( a good thing because it adds more challenge )

-Makes it feel more like a  horror game

-Makes even normal mode feel hard

Cons:

None

Conclusion:

In conclusion, This mod is a masterpiece. If valve makes a Left 4 Dead 3, They should take lessons from you.